Many circuits are commonly used for electronic devices wherein it is important that a rapid transition be made from one voltage level to another. Such a typical output circuit for a TTL gate might normally have a low voltage level input and a high voltage output. If a high voltage input occurs, it is important that the output circuit provides a very fast transition to a low output. It is also important that such output circuits be able to drive high capacitive loads and that a high impedance tri-state output also be provided.
Previously developed output circuits for TTL gates have been developed with "speed up" elements which apply extra speed up current to an output transistor during output transition. However, such prior speed up circuits do not apply speed up current for a sufficiently long time or of a sufficiently high magnitude, and also such previously developed speed up circuits often cannot be used as a high impedance tri-state circuit.